The present invention relates to a start control device provided to a compression self-ignition engine for combusting, by self-ignition, fuel injected from a fuel injection valve into a cylinder. The start control device automatically stops the engine when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, restarts the engine by injecting the fuel from the fuel injection valve while applying a torque to the engine by using a starter motor.
In recent years, compression self-ignition engines represented by diesel engines have become widely known as in-vehicle engines for reasons of their generally excellent thermal efficiency and reduced discharge amount of CO2 compared to spark-ignition engines, such as gasoline engines.
For a larger reduction of CO2 in such compression self-ignition engines, it is effective to adopt the art of a so-called idle stop control of automatically stopping the engine under an idle drive and then restarting the engine when a starting operation of the vehicle is performed. Various studies relating to this have been performed.
For example, JP2009-062960A discloses a control device of a diesel engine that stops the diesel engine when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, restarts the diesel engine by injecting fuel while driving a starter motor. With the control device, a cylinder to which the fuel is injected first is changeably set based on a stop position of a piston of a cylinder that stops on a compression stroke (compression-stroke-in-stop cylinder).
Specifically, in JP2009-062960A, when the diesel engine is automatically stopped, the stop position of the piston of the compression-stroke-in-stop cylinder that is on the compression stroke at the time is obtained, and it is determined whether the piston stop position is an appropriate position set relatively on a bottom dead center (BDC) side. When the piston stop position is the appropriate position, the fuel is injected into the compression-stroke-in-stop cylinder first so as to restart the combustion when the engine overall reaches a top dead center on compression stroke (compression TDC) for the first time in the restart (hereinafter, referred to as “the first compression start”).
On the other hand, when the piston of the compression-stroke-in-stop cylinder is on the TDC side of the appropriate position, the fuel is injected into a cylinder that is stopped on an intake stroke (intake-stroke-in-stop cylinder) when the cylinder shifts to the compression stroke so as to restart the combustion when the engine overall reaches the compression TDC for the second time in the restart (hereinafter, referred to as “the second compression start”). The second compression start in which the fuel is injected into the intake-stroke-in-stop cylinder instead of the compression-stroke-in-stop cylinder is because, when the piston of the compression-stroke-in-stop cylinder is on the TDC side of the appropriate position, a compression margin (stroke amount to the TDC) of the piston is small and air inside the cylinder does not increase sufficiently, causing a possible misfire even if the fuel is injected into the compression-stroke-in-stop cylinder.
With the art of JP2009-062960A, although the engine can be restarted promptly by the first compression start when the piston of the compression-stroke-in-stop cylinder is at the appropriate position, the second compression start is required when the piston is on the TDC side of the appropriate position, and it takes a long time to restart the engine. Thus, in the second compression start, because the fuel is injected after the intake-stroke-in-stop cylinder shifts to the compression stroke, energy generated by the combustion cannot be used until the engine overall reaches the compression TDC the second time in the restart, and a restart time period accordingly becomes long. Therefore, it has been desired to enable an engine restart by the first compression start as frequent as possible.